1. Field of the Invention
The present invention relates to the resurfacing or treatment of skin using biocompatible materials in a droplet or crystalline form that are propelled into the surface of the skin.
2. Description of Related Art
Resurfacing the human skin can be achieved by several mechanisms that are aimed primarily at disrupting the epidermal and upper dermal layers. Human skin is composed of at least three layers of variable thickness, depending upon body location. The uppermost layer, or epidermis, is usually as thin as a sheet of paper. The layer just below the epidermis is the dermis, which is largely composed of collagen and makes up the "leather" layer of the skin. The dermis may vary in thickness from that of paper (50-100 .mu.m) to as thick as half an inch on the neck and back. The layer below the dermis may be composed of either muscle (around the eyes and mouth) or fat, otherwise known as subcutaneous fat.
New human surface skin is regenerated following resurfacing by the surrounding islands of normal epidermis and epidermal cells migrating from the deep hair pores and other pore structures that permeate the upper dermis, mid dermis, and epidermis. If excessive scar tissue, rather than a plethora of epidermal cells, closes a surface wound, then an unsightly scar will result. The key to all resurfacing procedures is a controlled destruction of the desired area that still allows the regeneration of new tissues from pores and neighboring islands of untouched, untreated skin.
The procedures currently used in human skin resurfacing include chemical peeling, dermabrasion, laser surgery, and most recently the "power peel" or crystalline peel. In chemical peeling, a caustic, disruptive or destructive liquid agent is applied to the surface skin to damage existing epidermal and dermal cells, which will then be replaced by the body. Peeling agents act depending on their strength and type. Examples of chemical peeling agents include fruit acid peel, glycolic acid peel, and trichloracetic acid (TCA) and phenol peels. TCA peels can be made to act at deeper and varying depths by varying the concentration of TCA used to destroy the surface skin. Concentrations as low as 5-10% TCA will behave similarly to a fruit acid peel, and concentrations of 50% TCA may cause severe peeling burns, which simulates phenol, and may border on scarring. Phenol, when diluted with water, penetrates more deeply and destroys more tissue than most other peeling agents.
Dermabrasion literally means abrasion of the skin and is a procedure in which a rotating sanding wheel, or abrasive substance, is applied to a rigidified skin to sand out an undesirable feature, mark, or scar. Some high-speed dermabrasion rotors go up to 200,000 revolutions per minute (rpm) and do not require any rigidity to the tissues; however, they require extremely skilled personnel and special instrumentation and are impractical for most office use. A minor mistake with such a high powered machine can have disastrous results. Dermabrasion is usually performed with a rotating wheel operating at speeds under 10,000 rpm after the skin has been rigidified using freon or dichlorotetrafluoroethane. In dermabrasion (unlike laser surgery), the person operating the abrading wheel has a direct tactile sense of pressing the wheel into the tissues being treated and can apply differential pressure to areas of elevation. Dermabrasion can be achieved to various depths depending upon the depth of freezing (rigidification), the number of passes of the abrader, the type of abrasive wheel, and the pressure applied. This procedure is waning in use, however, due to the unavailability of freon.
Laser surgery has recently become popular to remove or reduce wrinkles, remove tumors, and alter scars, although results are mixed. Several types of lasers are used, including carbon dioxide and erbium-YAG lasers. Carbon dioxide lasers deliver light radiation at 10 .mu.m, which can vaporize and destroy surface skin. These lasers may be set on various pulse patterns to deliver precise and controlled amounts of laser radiation to the skin in a relatively uniform and homogenous fashion across the surface. An unfortunate disadvantage of this laser is that heat can be transmitted to the surrounding tissues. Additionally, after the first pass of the carbon dioxide laser, the skin begins to ooze and become wet at the surface as fluids build up in response to the damage. Since water and blood absorb in the infrared region, a second pass of the laser will penetrate to a variable depth, depending on how much surface ooze there is in the area. The ooze prevents the laser energy from reaching the target tissues uniformly. During laser irradiation, the tissues may begin to desiccate, which ultimately results in severe thermal damage. Depositing too much laser energy on the target tissues can result in persistent redness, scarring, and other complications or damage, even with thermal relaxation techniques to mitigate heat transfer.
Although other lasers, such as the erbium-YAG laser or combination CO.sub.2 /erbium laser, were developed in an attempt to reduce bleeding and thermal damage, serious scarring and persistent redness can still result. If the penetration depth of the damage is complete and the regenerating skin structures are destroyed, scarring will ensue. Scarring is the unwanted presence of large amounts of collagen in the upper surface, with a minimal amount of normal appearing epidermis to lend a normal appearance to the skin. When scars are treated with certain lasers, the light does not actually remove or destroy collagen, but usually affects the hemoglobin and other blood pigments. The reduction of blood vessels to the scar causes an optical effect that makes the scar less noticeable.
The power peel is relatively new in the United States and is basically a method of "sandblasting" the skin. This procedure has been touted to reduce acne scars and remove all other types of scars and imperfections. The power peel is a process by which aluminum oxide crystals, which are extremely hard, are shot at the skin with 25 psi of air pressure. Safe operation of these devices requires the use of a limited number of passes or accurate control of pass speed to the target area. A power peel that only removes the epidermis of the skin will not result in any alteration of scar formation and produces very little long-lasting cosmetic effect. However, aluminum oxide crystals that are shot deeply enough into the skin to remove or alter deeper structures such as scars or pits can cause granuloma formation or foreign body reaction because aluminum oxide crystals are not biocompatible. Thus the body extrudes or encapsulates unwanted particles at levels of skin where protection is necessary, which may lead to disease and unsightly scarring. Even systems that include a vacuum apparatus to suck away unwanted particles do not remove 100% of the particles. Even a small amount of residue crystals can lead to disease and other cellular difficulties.
Thus, it would be advantageous to develop a procedure that can remove scars, wrinkles, and various other imperfections or lesions on the skin without introducing foreign bodies or substances that cause adverse physiological reactions or produce thermal damage. The present invention addresses this problem by using materials that are harmonious with the human body.